China's service sector is still growing, but growth slowed in December to its weakest level since August 2011, the British bank HSBC reported on Monday.

The Purchasing Managers' Index for December came in at 50.9, down from November's index of 52.5. Any index number above 50 indicates growth in business activity. A reading lower than 50 means contraction.

Service providers signaled modest growth in new orders in December, although it was the weakest showing in six months, according to HSBC.

Purchasing managers in service-related businesses showed historically weak positive sentiments about the 2014 business outlook. In December, only 26 percent of the survey’s respondents expected output to increase.

Despite the moderate overall expansion of the sector, service workforce numbers showed their strongest expansion since June, the bank said.

The HSBC Service PMI was in line with the official data, which reported a four-month low of 54.6 in December, following 56 in November, 56.3 in October and 55.4 in September

Qu Hongbin, chief economist in China for HSBC, said he expected the service sector to get some help in the year ahead.

"We expect the steady expansion of manufacturing sectors to lend support to service sector growth," he said.

"Moreover, the implementation of reforms, such as lowering the entry barriers for private business in service